1. Field of the Invention
The present invention relates to an optical device using an electroactive polymer actuator as an actuator of a blur correcting unit.
2. Description of the Related Art
In recent years, widespread use of subminiature cameras mounted in digital or cellular telephones has resulted in an increasing demand for optical devices, such as cameras and video cameras, that are small and that provide high performance. When cameras or video cameras are reduced in size, the influence of vibration that they receive due to, for example, motion blurring is increased, thereby resulting in frequent blurring of a picked up image. Therefore, demand for a blur correcting mechanism is increasing. Hitherto, an electromagnetic motor has generally been used as an actuator for a driving mechanism of a blur correcting unit. The electromagnetic motor comprises a coil and a magnet, and converts electrical energy into driving power on the basis of what is called “Fleming's Law,” as a result of supplying electric current through the coil in the magnetic field of the magnet. A position detector, such as a light-receiving element, is used as a sensor that detects a driving displacement of the electromagnetic motor. To reduce the size of the actuator used as the electromagnetic motor, it is necessary to increase driving power that is generated per volume of the actuator. However, when the driving power is increased, the magnetic field needs to be increased. More specifically, a large driving power can be generated by any one of the following methods:
(1) Passing a large current as a result of increasing the diameter of the coil;
(2) Increasing the number of windings of the coil; or
(3) Increasing the magnetic flux density as a result of increasing the size of the magnet.
However, when these methods are used, the electromagnetic motor is increased in size, thereby increasing the amount of electric current consumed and requiring a sophisticated controlling system. Therefore, there is a limit as to how small the electromagnetic motor can be made when these methods are used.
In addition, driving noise of the motor, itself, and noise of, for example, a gear (which is a mechanism for transmitting the driving power of the electromagnetic motor) are generated. Further, the mechanism has a sliding portion, thereby reducing the durability of the mechanism.
In recent years, research is being conducted on high polymeric materials, which have high generative force per volume and high strain, themselves, to apply the high polymeric materials to, for example, artificial muscles. An actuator (electroactive polymer actuator) to which high polymeric material is applied is available.
The electroactive polymer actuator is compressed in the direction of an electric field by electrostatic force that is generated between electrodes by applying voltage between the electrodes. At the same time, it is stretched perpendicularly to the electric field to produce pressure, so that it is possible to increase the strain of the polymeric material, itself, and the output per volume. Therefore, the pressure and strain can be provided by direct driving, thereby making it unnecessary to use a mechanism, such as a displacement enlarging mechanism or a speed reduction mechanism, such as a gear box, required in, for example, related motors. Consequently, it is possible to reduce the size, costs, and noise, and to achieve proper durability. In addition, as disclosed in, for example, U.S. Pat. No. 6,809,462, if a change in electrostatic capacitance caused by a displacement of the electroactive polymer actuator is detected by a sensor circuit, the electroactive polymer actuator can be used as a sensor. A circuit for detecting a change in electrostatic capacitance, such as a resonator-type circuit, is widely known, so that a related circuit may be used for the circuit for detecting a change in electrostatic capacitance.
Japanese Patent No. 3501216 gives examples in which an electrostrictive stretching-and-contracting material is used in, for example, a valve device, a pump device, an actuator device, a sensor device, a generating device, and a vibratory driving device.
U.S. Pat. No. 6,891,317 discloses a cylindrical electroactive polymer actuator which is stretched and contracted in an axial direction thereof.